Two former Parramatta Eels players are accused of harbouring semi-automatic weapons and possessing more than half-a-million dollars in cash after dramatic arrests in Sydney's Centennial Park yesterday.

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"We know he's in a vulnerable mental state and the incident this morning - being arrested and taken to the airport and separated from his lawyer - would have been quite traumatic in any circumstances," Kate Schuetze from Amnesty International told AAP.

"I'm very concerned right now that the authorities will try to arrest, detain or question him, which would be the worst possible thing for his health and wellbeing."

His case is extreme and he must not be left to languish on Manus Island, Amnesty says.

The Australian government pushed the young man into a desperate position and must now take responsibility for Mr Sawari and bring him to safety, the group says.

Australian immigration officials would not be drawn on whether they'd been involved in the matter or would be once Mr Sawari was back in PNG.

"The settlement of refugees in PNG is a matter for the PNG government," a department spokesman said.

"The reception and processing of refugee claims in Fiji is a matter for the Fijian government."